This invention relates generally to electrical apparatus and more particularly to a support system for a gas-air termination.
Compressed gas-insulated transmission lines are being used in an ever increasing scale in recent years due to the desirability of increasing safety, problems in acquiring the necessary right-of-way for overhead lines, and higher power loads required by growing metropolitan areas and growing demands for electrical energy. Gas-insulated transmission lines typically comprise a hollow outer sheath, an inner conductor disposed within the sheath, a plurality of solid insulating spacers which support the conductor, and a compressed gas such as sulfur hexafluoride in the outer sheath for electrically insulating the inner conductor from the outer sheath. Gas barriers may be provided at intervals along the length of the transmission line for isolating the various sections on the line, and it is known to provide a particle trap as it is disclosed in the patent to Trump, U.S. Pat. No. 3,515,939.
Th majority of gas-insulated transmission lines installed to date have generally been for electric power station getaways or high-voltage transmission line dips. In these types of installations, the gas-insulated transmission line is connected to overhead power lines which then transmit the energy where desired. The connection of the gas-insulated transmission line to the overhead power line generally occurs through an gas-air termination. These terminations are generally positioned at elevations approximately that of the overhead transmission line, so that the termination is disposed vertically above the ground. The vertically disposed termination must then be interconnected to the gas-insulated transmission line, which in the majority of installations, will be disposed generally horizontally.
One disadvantage which has been found with this type of installation is providing the necessary support for the elevated gas-air termination. Since the termination is disposed off the ground, a support structure must be utilized to maintain the termination in its spatial location. The problem arises in that the generally horizontally disposed transmission line will typically experience longitudinal or horizontal movement due to thermal expansion of the line itself. The support for the air termination must, therefore, not only provide vertical support for the termination, but also allow for horizontal or longitudinal movement thereof to compensate for the thermal expansion of the transmission line.
The prior art structures utilized to support the gas-air termination generally are elevated structures having large openings therein at the top thereof. These structures are disposed vertically lower than the termination, with the transmission line connection to the horizontally disposed transmission line extending through the opening of the support structure. The support structure opening is larger than the transmission line, and is larger a distance which will allow for the longitudinal movement of the connection due to horizontal expansion of the transmission line proper. The outer shell of the termination then rests upon the support structure to maintain its elevated position.
A drawback with this type of support is its large expense. When phases of a three-phase transmission system are separated for the normal air clearances for the overhead transmission line, separate, distinct structures must be utilized for supporting each gas-air termination. The cost of erection, and the materials required in their construction, are expensive, and it is desirable to provide a more economical support means for supporting the gas-air termination.